Zonally averaged meridional circulations Hadley Cell WEST WINDS EAST WINDS MERIDONAL Egustor CRCULAION EAST WINDS H EAST WINDS WEST WINDS 授课教师：张洋3授课教师：张洋 3 Zonally averaged meridional circulations - Hadley Cell A brief history of the Hadley circulation A brief history of the Hadley circulation 1. Hadley’s circulation model (1735) Greater solar heating in low latitudes lead to rising motion near the equator and sinking near the poles, with equatorward motion at low levels and poleward motion at low levels and poleward motion aloft completing the circuit. Because of the conservation of absolute velocity, the equatorward motion at low l l t t d h ii t levels turns westward when arriving at high latitudes and forms the trade wind. Hadley did not realize that the conservation involved is absolute ang , ular momentun, rather than velocity. He was also unaware of the effect of the Coriolis force, which would turn the poleward flow westerly. flow westerly. However, there is no simple argument eliminating the possibility of a single direct cell in each hemisphere, with or without the earth’s rotation 7 without the earth s rotation